The present invention relates to shutter mechanisms for shutters, elevators, or the like, and in particular to improvement of the stopping control at the upper and lower limit positions of an object to be wound and unwound by using the detected magnitude of a load generated at a motor used to wind and unwind the object.
Shutter mechanisms such as the one disclosed in Japanese unexamined patent application 2002-332788 are equipped with a shutter main unit having multiple hinged plates, a drum around which the hinged plates are wound, a motor that rotates the drum, and a speed reduction mechanism. This type of shutter mechanism is typically installed at the top of entrances and exits of shops, factories, or the like, and the motor rotates the drum to open and close the entrance/exit by respectively winding and unwinding the hinged plates. In general terms, the shutter mechanism described herein, and particularly the stepping motor control apparatus, may be used for controlling any stepping motor used in an application requiring accurate bi-directional control of first and second stopping positions of an object that is moved thereby.
More specifically, the motor of the shutter mechanism is typically activated by the push of a button located on, for example, a wall inside the entrance/exit. When the button is pushed, a controller controls the current provided to the motor to thereby cause the motor to rotate the drum in a forward direction to unwind the shutter, to rotate the drum in the reverse direction to wind the shutter, or to stop. Furthermore, sensors detect the upper limit position for winding the shutter main unit and the lower limit position for unwinding the shutter main unit. The detection results are input into the controller, and the controller then stops the motor based on the detection results.
In a shutter mechanism such as the one described above, the motor rotor continues to rotate briefly due to inertia even after the controller stops the current to the motor. As a result, there is a time lag until the motor stops completely, reducing the precision of the position wherein the shutter main unit comes to rest. In addition, a shutter mechanism that includes the sensors for sensing the upper limit position for winding the shutter main unit and the lower limit position for unwinding the shutter main unit requires additional parts, and the assembly required to place the sensors in the location wherein the shutter mechanism will be used is complicated and time-consuming.
A brake mechanism can be provided on the drum, and a speed reduction mechanism may be connected to the drum through a clutch, in order to increase-the accuracy of the position where the shutter main unit comes to rest. However, such a brake mechanism would require an even higher number of parts, and would further increase the cost of manufacturing and assembly of the shutter mechanism.